Problem accessing CMS after install

I installed silvertripe v2.0.2b on a debian system with lighttpd. After installation
I get the welcome page, but when I enter the CMS, I get following error:
user_error(None of these templates can be found: Security_dologin.ss, Security.ss,512)
line 53 of SSViewer.php

SSViewer->__construct(Array)
line 193 of Controller.php

Controller->getViewer(dologin)
line 161 of Controller.php

Controller->defaultAction(dologin,Array)
line 136 of Controller.php

Controller->run(Array)
line 48 of Director.php

Director::direct(Security/?executeForm=LoginForm)
line 101 of main.php